1. Field of the Invention
This invention relates to a wafer chamfering machine for performing chamfering work on a wafer such as silicon serving as a raw material for a semiconductor element, and more particularly to a wafer chamfering machine, in which chamfering of the outer periphery and a notch of the wafer is performed by the same wafer chamfering machine.
2. Description of the Related Art
The wafer such as silicone serving as the raw material for the semiconductor element is produced in a way that the wafer is cut into a thin piece from a state of an ingot, and thereafter, the outer periphery thereof is chamfered by use of a wafer chamfering machine. Furthermore, there is a case where a notch is formed in the wafer in association with the direction of a crystal of silicone and also chamfering is performed on this notch.
FIG. 2 shows an outer appearance of the wafer provided therein with the notch. In FIG. 2, designated at D is the diameter of the outer periphery 11 of the wafer, .alpha. an opening angle of a notch 12, .delta. an inclination of the center of the notch 12 to the center of the outer periphery 11 of the wafer and L is a distance from the outer periphery 11 of the wafer to the notch 12 (A circle shown at the portion of the notch 12 is the circle representing the measured value, but not a part of the wafer).
Furthermore, FIG. 3 shows chamfering shapes required for the outer periphery 11 and the notch 12 of the wafer.
FIG. 3 shows that Bu and Bd are widths of chamfering; .theta.u and .theta.d are tapered angles; Ru and Rd have curved corners and t has a flat outer periphery (not pointed). T is a thickness of the wafer. As grindstones for chamfering work, a trapezoidal type grindstone 31 is used as shown in FIG. 4 or a formed grindstone 51 shown in FIG. 5. The dimensions and shapes shown in FIGS. 2 and 3 have tolerances, and, when the dimensions and shapes come off the tolerances, defectives will be resulted.
Methods of performing the chamfering work shown in FIGS. 2 and 3 include a method of performing the chamfering work by use of a chamfering machine specialized for chamfering the outer periphery and a chamfering machine specialized for chamfering the notch and another method of chamfering by use of a chamfering machine for chamfering the outer periphery, which is separately provided therein with a notch chamfering work station.
However, the conventional chamfering method presents a problem in that, since it is difficult to accurately position the notch 12 relative to the diameter D of the outer periphery 11 of the wafer, it is difficult to accurately perform chamfering work of the dimensions and shapes of the notch 12 relative to the diameter D of the outer periphery 11 of the wafer. Furthermore, there is another problem in that, since the separate chamfering machines are required required the work station, is required separately, the space for the chamfering machine or machines is increased in size the cost is increased. Further, there is another problem in that, since the works are required twice for mounting the wafer to a wafer table for positioning, vacuum drawing and the like and for removing the wafer from the wafer table after completion of work, much time is required for performing each procedure.